Cloning one of the first-studied genes -- Mendel's tallness gene -- gives scientists new insight into plant physiology

Plant scientists from Cornell and the University of Tasmania, Australia, have successfully cloned one of history's first-studied genes -- the gene for stem growth in peas, according to a report in the latest issue of journal The Plant Cell, which was published today.

Cloning the gene gives scientists a new way to account for why some plants are tall and some are short.

"This is one of the most important genes in history as it illustrates the principles of genetics," said Peter Davies, Cornell professor of plant physiology, who worked on this research during a recent sabbatical in Australia.

In a monastery more than 130 years ago, in what is now the Czech Republic, Augustinian monk Gregor Mendel selected seven distinct characteristics of pea plants and traced how those characteristics were passed through generations. One of the principal traits on which he worked was stem length, the primary determinant of plant height.

The plant scientists working at the University of Tasmania, Hobart, Australia, isolated, cloned and obtained the DNA sequence of Mendel's historic tallness gene, and showed that it codes for gibberellin 3-beta-hydroxylase, a biosynthetic enzyme crucial to the division and elongation of the cells in the plant's stem.

Researchers Diane R. Lester, a molecular biologist; John J. Ross, a plant physiologist and James B. Reid, professor of genetics, all at the University of Tasmania, and Davies, will publish "Mendel's Stem Length Gene (Le) Encodes a Gibberellin 3b-Hydroxylase" in the August issue (Vol. 9, published August 26, 1997) of The Plant Cell, the journal of the American Society of Plant Physiologists.

In 1984, the Tasmanian group demonstrated that tallness in pea plants is regulated by an acid called gibberellin, or GA1, with promotes stem growth. Gibberellic acid had been discovered in the 1950s, but it was not until the early 1980s that the group connected it to stem height.

Now, the researchers have demonstrated that in the tall pea plants used by Mendel, the tallness gene codes for an enzyme that adds a hydroxyl (HO) group at a very particular location onto GA20, which is the is the immediate precursor of GA1.

In the dwarf plants there is a change of one base in the DNA sequence, which leads to a change of one amino acid in the resulting protein. In turn, this results in an enzyme that is still active in converting GA20 into GA1, but at 1/20th the rate. Therefore, dwarf peas are less efficient at synthesizing the gibberellic acid responsible for promoting stem growth. The plant becomes growth deficient.

Gregor Mendel (1822-1884), the father of genetics, conducted experiments on the hybridization of plants, particularly peas. The results of his research were included in two lectures delivered in 1865 to the Natural History Society of BrŸnn, Davies said. Subsequently, Mendel published a long paper in an 1866 issue of the Proceedings of the Natural History Society. Mendel's description of units of heredity, the formulation of the Laws of Segregation and Independent Assortment, and his coining of the concepts of dominant, recessive, and discrete factors -- later called genes -- remain the foundations of genetics today.

Little attention was drawn to Mendel's work in his own lifetime, Davies said. At the turn of the century, the Royal Horticultural Society of Great Britain commissioned an English translation from German of Mendel's work, and it was published in 1901. News of the findings spread. His work was highlighted at the International Conference on Plant Breeding and Hybridization, which met in New York City in 1902.

Davies said a review of the conference showed that many plant breeders had never heard of Mendel or his experiments. They were excited by the "new" findings and soon put theory into practice. From these humble beginnings, genetics and later molecular biology, evolved.

"Mendel's experiments are now included in every high school biology class," said Davies.